1. Field of the Invention
The present invention relates to a positive resist composition suitable for use in the ultramicrolithography process such as production of VLSI or a high-capacity microchip or in other photofabrication processes. More specifically, the present invention relates to a positive resist composition capable of forming a high-resolution pattern by using electron beam, EUV or the like, that is, a positive resist composition suitably usable for fine processing of a semiconductor device, where electron beam or EUV light is used, and a pattern forming method using the same.
2. Description of the Related Art
In the process of producing a semiconductor device such as IC and LSI, fine processing by lithography using a photoresist composition has been conventionally performed. With the recent trend toward high integration of an integrated circuit, it is becoming necessary to form an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using electron beam, X ray or EUV light is proceeding.
The lithography using electron beam or EUV light is positioned as a next-generation or next-next-generation pattern formation technique and a high-sensitivity positive resist is being demanded.
In particular, the elevation of sensitivity is very important for shortening the wafer processing time. A chemical amplification-type positive resist generally comprises a resin insolubilized to alkali by protecting the alkali-soluble group with an acid-decomposable group, a photoacid generator and a basic compound. The photoacid generator is decomposed upon exposure to generate an acid, and this acid decomposes the acid-decomposable group while diffusing in the resist film, whereby the resin is insolubilized to alkali. Accordingly, in order to elevate the sensitivity, it is preferred to encourage the acid to diffuse and cause a deprotection reaction.
On the other hand, a process margin such as exposure latitude (EL) is also an important factor in view of performance. EL is known to deteriorate when an acid diffuses.
The amount of deprotection per the number of acids generated is preferably increased for achieving high sensitivity, but this at the same time involves diffusion of an acid and therefore, it is a difficult technical problem to realize both high sensitivity and high EL.
For realizing high sensitivity while suppressing the diffusion of acid, it is considered to be effective to elevate the acid generation efficiency. This may be attained if the decomposition efficiency or concentration of the photoacid generator can be raised, but when the concentration of the photoacid generator is raised, there may arise a problem that the photoacid generator aggregates, deteriorates in the aging stability or precipitates.
U.S. Pat. No. 5,561,194, JP-A-2001-166474 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2001-166478, JP-A-2003-107708, JP-A-2001-194792 and JP-A-2005-234434) each discloses a photoresist composition using a phenolic acid-decomposable resin obtained by copolymerizing an acid-decomposable acrylate monomer having an alicyclic group as an acid-decomposable group.
U.S. Patent Application Publication No. 2007/0248908 discloses a resist containing a resin, an acid generator, a basic compound and a solvent each in a predetermined amount, where the resin is a copolymer of a hydrophilic monomer with the polar group being partially protected by an unstable group with a low activation energy and a hydrophobic monomer having an aromatic cyclic group.
JP-A-2007-210904 discloses a photosensitive composition containing a specific sulfonium salt as an acid generator with an attempt to improve the sensitivity, resolution and pattern profile and solve the problems of roughness and out-gas.
JP-A-2004-271629 discloses a positive resist composition containing a specific resin and a sulfonic acid generator, where the concentration of the sulfonic acid generator is specified.